By JOHN KNAPP, Vice President of Air
Control Solutions, Ruskin, Grandview, Mo.
Fire Dampers and Smoke Dampers:
The Difference is Important
The most effective fire protection plans include detection, suppression and containment requiring both active and passive fire protection. Active fire protection includes
all systems designed to suppress or extinguish fire once it has started, as well as aid in
the evacuation of occupants. These include smoke detectors, building pressurization, fire
alarms, sprinklers, exit signs, and evacuation plans. However, active fire protection
systems do not prevent the spread of smoke and toxic gases, the leading cause of death
from fire. Passive fire protection is designed to prevent smoke, toxic gases, and fire from
spreading; and by compartmentalizing fire, passive fire protection systems:
•
•
•
•
Strengthen the effectiveness of active systems
Facilitate occupant evacuation
Protect property
Minimize property damage
Compartmentalizing the building with fire-rated separations like fire walls, fire barriers,
fire partitions, smoke barriers, and smoke partitions is a critical feature of the system.
When penetrating these walls or partitions by the ductwork of the heating, ventilation,
or air conditioning (HVAC) system, the integrity of their ratings are sustained by the
use of fire dampers, smoke dampers, or combination fire/smoke dampers. These three
damper types perform different functions and are installed and maintained differently
as well. Knowledge of these differences is imperative to the proper application of the
dampers and their performance in the life/safety system.
A fire damper closes once the duct temperature reaches a high enough level to melt a
fusible link. A smoke damper closes upon the detection of smoke. The codes have recognized, and most engineers agree, that the best method of compartmentalization is
through the use of the combination fire/smoke damper. It closes not only upon high duct
temperature but also upon the detection of smoke. The combination fire/smoke damper
can ship with override controls to pressurize individual spaces. It is UL leakage-rated to
stop smoke in its tracks, which is a main difference from fire dampers. Only combination
fire/smoke dampers or stand-alone smoke dampers are leakage-rated devices (Table 1).
Table 1: Underwriters Laboratories Standard UL555S Leakage Classifications
Leakage Classification
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Leakage, cfm/sq-ft at Standard Air Conditions
4.5 in. wg.
8.5 in. wg.
12.5 in. wg.
I
8
11
14
II
20
28
35
III
80
112
140
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Fire Dampers
A fire damper can be defined as “a device installed in ducts and
air transfer opening of an air distribution or smoke control system designed to close automatically upon detection of heat. It
also serves to interrupt migratory airflow, resist the passage of
flame, and maintain the integrity of the fire rated separation.”1
Its primary function is to prevent the passage of flame from one
side of a fire-rated separation to the other.
Figure 1: Example of a curtain-blade fire damper with
fusible link and factory integral sleeve. Photo courtesy
of Ruskin.
Fire dampers (Figure 1) are operated by a fusible device, typically a melting link. They are designed and tested under UL
Standard 555: Standard for Safety for Fire Dampers, to maintain the integrity of the fire-rated separation. Fire dampers are
equipped with a fusible link (rated for 165°F up to 286°F),
which holds the blades open until it the link melts. Upon reaching the melting point, the blades then close and stop the flame
from moving into an adjoining compartment.
Location: Fire dampers are installed in or near the wall or
floor, at the point of duct penetration, to retain the integrity and
fire rating of a wall or floor whether it is a ducted or open-plenum return application. Should the ductwork fall away, the
damper needs to stay in the wall or floor to maintain the integrity of the wall or floor. One should actually think of the fire
damper as part of the wall system itself.
Sleeves and Attachment: Fire dampers are required to be
installed in sleeves. Lighter gauge sleeves (18–20 ga.)
require a breakaway connection from the sleeve to the ductwork. Heavier, smaller dampers (16 ga.) can be installed with
a hard duct connection. The manufacturer’s installation
instructions will include the approved method for attachment
and spacing of the attachment (Figure 2).
Figure 2: Typical fire damper installation, based on AMCA
503, Fire, Ceiling (Radiation), Smoke and Fire/Smoke
Dampers Application Manual. Image courtesy of Ruskin.
Sealing: The spaces between the damper frame and the duct
typically are not sealed due to thermal expansion. Breakaway
connections as well as other seams can be sealed if the
manufacturer’s listing includes a UL-approved sealant.
There are two types of applications for fire dampers: static and
dynamic. Static fire dampers can only be applied in HVAC
systems that are designed to shut down in the event of a fire.
Dynamic fire dampers have been tested for closure under airflow and carry both an airflow velocity (fpm) and pressure
differential rating. The minimum rating for all dynamic fire
dampers is 2,000 fpm and 4.0 in. wg. The minimum ratings
are based upon closure at a minimum airflow of 2,400 fpm and
4.5 in. wg.
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Figure 3: Example of a typical smoke damper.
Photo courtesy of Ruskin.
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Standards With Post-Installation Guidance
In addition to the two applications, fire dampers are also available in two basic designs: curtain-type and multiple-blade-type.
Curtain-type dampers are the most common and consist of a
“curtain” held up by a fusible link. Multiple-blade dampers are
similar to control dampers with “blades” located in the airstream. Multiple-blade fire dampers generally offer greater
restriction to airflow than a curtain-type fire damper for the
same size duct. However, multiple-blade fire dampers can be
applied in situations when the system air velocities exceed the
curtain-type fire damper closure ratings. Multiple-blade fire
dampers have been UL tested and are “dynamic” rated for closure at 4,000 fpm and 8.0 in. w.g.
Figure 4: Example of a combination fire/smoke damper
with electric heat release device. Photo courtesy of Ruskin.
however, fire/smoke dampers are available with electric heat release devices instead of fusible links. The electric release devices
are resettable and allow the damper to close in a controlled manner rather than slamming closed and causing pressure problems
in the HVAC system.
Smoke Dampers
Smoke dampers (Figure 3) are defined as “a device installed in
ducts and air transfer opening of an air distribution or smoke
control system designed resist the passage of air and smoke.
The device operates automatically and is controlled by a smoke
detection system. They can be opened or closed from a remote
fire command station if required.”1 Their primary function is to
prevent the passage of smoke through the heating, ventilation,
and air conditioning system, or from one side of a fire-rated
separation to the other.
Smoke dampers are operated by either a factory-installed electric or a pneumatic actuator. They are controlled by smoke
detectors and/or fire alarms. Smoke dampers are qualified under
UL Standard 555S, UL Standard for Safety for Smoke Dampers,
and have two general applications:
1.As part of a “passive smoke control system” in which they
close upon detection of smoke and prevent the circulation
of air and smoke through a duct, transfer, or ventilation
opening.
2.As part of an “engineered smoke control system” designed
to control smoke migration using walls and floors as barriers to create pressure differences. Pressurizing the areas
surrounding the fire prevents the spread of smoke into
other areas.
Smoke dampers have the following installation requirements:
Location: Smoke dampers are for use in or adjacent to smoke
barriers. They must be installed no more than 24 in. from the
smoke barrier. Of course, smoke dampers that are used to isolate air handlers are not limited to this distance requirement.
NFPA 90A states that smoke dampers are to be used to isolate
air handling units over 15,000 cfm.
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Figure 5b: An “out of the wall/
partition” fire damper installed on a
2-hour-rated steel/gypsum firewall.
Photo courtesy of United Enertech.
When designing damper systems for fire and smoke protection, engineers
need to consider how they will be tested and maintained over the years they
will be in place. Two standards published by the National Fire Protection
Association (NFPA) provide operation, maintenance, and testing requirements: Chapter 6 of NFPA 105-2010, Standard for Smoke Door Assemblies
and Other Opening Protectives, and Chapter 19 of NFPA 80-2010, Standard
for Fire Doors and Other Opening Protectives. Together, these standards
cover operational testing and inspection immediately after installation;
periodic inspection and testing; and maintenance of smoke dampers,
fire dampers, and combination fire/smoke dampers. They also include
requirements for documentation of the inspection, tests, and maintenance.
Figure 5a: Example of an "out of the wall/partition"
combination fire/smoke damper. Photo courtesy of Pottorff.
Sleeves and Attachment: Smoke dampers do not necessarily
have to be installed in sleeves. They can be installed directly
in the duct. The manufacturer’s installation instructions will
include the approved method for attachment and spacing of
the attachment.
Sealing: The joints between the damper frame and the duct
must be sealed to prevent unwanted air leakage. Smoke damper
leakage ratings are based on leakage through the blades and
inside damper frame and not on additional leakage between the
damper frame and duct or sleeve.
Combination Fire/Smoke Dampers
Combination Fire/Smoke dampers (Figure 4) meet the
requirements of both the UL Standards for Safety, UL 555 Fire
Dampers and UL 555S Smoke Dampers, and applications requirements as described above. They are used in HVAC
penetrations where a wall, floor, or ceiling is required to have
both a fire damper and smoke damper. They close upon the detection of heat (via duct temperature) or smoke (via a smoke
detector) and “seal” the opening. Unlike regular fire dampers,
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System designers should insist upon these electric fuse links
when selecting a combination fire/smoke damper. Models designed with airfoil blades perform better (less pressure drop)
than others. Less pressure drop in a system means energy savings. System designers should select products that certify their
performance through a third party, such as the Air Movement
and Control Association International (AMCA). Locations,
sleeve attachments, and sealing of combination fire/smoke
dampers follow the same criteria as fire dampers.
Important Note on Installation
The installation of life/safety dampers should always be accomplished in accordance with the manufacturer’s instructions
as tested by UL or another code-compliant approval agency.
Installation instructions provided by a manufacturer should
never be used to install the dampers of a different manufacturer
as the dampers may not have been tested to and passed the
specific installation. Recently, many damper designs, particularly combination fire/smoke dampers, have increased their
application and installation flexibility, including “out of the
wall/partition” installations (Figure 5a and 5b). The number of
UL tests performed on FSDs has increased dramatically to accommodate the new designs and installation methods. These
designs have made it easier to select and install the right damper without creating undue burden on the engineer, contractor,
and the local authority having jurisdiction (AHJ). Mechanical
inspectors and plan review teams are being educated on these
changes and are becoming increasingly aware of the new installation methods. Again, it is important that the damper
manufacturer’s approved installation sheets be available for
the AHJ during installation review.
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As with any building system, inspection and maintenance of
components is essential to proper operation. This is especially true of a fire/safety system! The National Fire
Protection Association NFPA 105: Standard for Smoke Door
Assemblies and Other Opening Protectives states each
damper shall be tested and inspected one year after installation. The test and inspection frequency shall then be every 4
years, except in hospitals, where the frequency shall be every 6 years. The code also states that the damper shall be
actuated and cycled. The inspections must be documented
indicating the location of the damper, date of inspection,
name of inspector, and deficiencies discovered.
Similarly, NFPA 80: Standard for Fire Doors and Other
Opening Protectives, states that fire and combination fire/
smoke dampers shall require inspection and testing one year
after installation. In addition, the testing and inspection frequency shall then be every 4 years, except in hospitals, where
the frequency shall be every 6 years. NFPA 80 also requires
documentation of the inspections.
The use, proper installation, and maintenance of fire, smoke,
and combination fire/smoke dampers in sprinkled or nonsprinkled buildings is a vital part of a properly designed life safety
system. When fire emergencies happen, the fire, smoke and
combination fire/smoke dampers will help contain the fire and
resulting smoke to the compartment of origin and thus minimize life and property loss while helping the firefighters
extinguish the blaze.
References
1. A
MCA Publication 503-03, Fire, Ceiling (Radiation), Smoke and
Fire/Smoke Dampers Application Manual, Air Movement and
Control Association International, 2003.
2.UL 555S, Standard for Safety—Smoke Dampers, Underwriters
Laboratories, June 1999.
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